Field of the Invention
The invention relates to a technology for image processing.
Description of the Background Art
A conventionally-known image display system generates images showing a vicinity of a vehicle, such as a car, and displays the generated images on a display in the vehicle. Users (mainly a driver) can recognize situations of the vicinity of the vehicle substantially on a real-time basis by using such an image display system.
An image display system is also known that generates an image showing the vicinity of the vehicle viewed from an arbitrarily-set virtual viewpoint, such as a point above the vehicle, using images acquired by capturing images of the vicinity of the vehicle and that displays the generated image. The image showing the vicinity of the vehicle viewed from the virtual viewpoint is generated by using data of a virtual projection plane acquired by projecting data of captured images onto the virtual projection plane corresponding to the vicinity of the vehicle. A shape of such a projection plane is generally a horizontal plane (road surface) in a horizontal direction.
However, in a case where the shape of the projection plane is the horizontal plane (road surface), the further an object exists from the vehicle, the further the object is projected on the projection plane. In a case of a 3D object, for example, a height of the 3D object is displayed higher than an actual height of the 3D object from the road surface. In other words, the 3D object is displayed, being deformed and seeming stretched longitudinally as compared to the actual 3D object. Such a phenomenon is specifically obvious in left, right, upper and lower end portions of the image.
In order to improve strangeness of the displayed image, a method is also well-known in which image data is projected, using a bent projection plane of which inclination becomes greater as a portion is further away from a position of the vehicle on the projection plane. In this case, a position onto which an image of a 3D object existing distant from the vehicle is projected is closer than a position onto which the image of the 3D object is projected in a case of projection onto a horizontal plane. Therefore, an image is generated, suppressing deformation caused by the longitudinal extension.
If such a projection plane is used, an upper center portion of the image is shrunk to suppress the deformation by the longitudinal extension, mainly, of the portion located further from the vehicle. Therefore, the image is not displayed in an upper center portion of a screen. In order to actually display the image on the display, an area other than the undisplayed area is extracted from the image and the extracted portion is displayed.
The greater an angle of the projection plane is, the greater a correction amount for suppressing the deformation by longitudinal extension is. Thus, the 3D object can be displayed with less strangeness. While, the greater the correction amount is, the greater an area in the upper center portion of the image is shrunk and the less displayable area is. In other words, extracted area is reduced. Thus, an area showing the vicinity of the vehicle is reduced and thus it is difficult to see the vicinity of the vehicle sufficiently. Therefore, it is necessary to strike a balance between the correction amount for suppressing the deformation by longitudinal extension and the displayable area. The correction amount for suppressing the deformation by longitudinal extension cannot be increased without consideration.
As described above, since the correction amount for suppressing the deformation by longitudinal extension cannot be increased enough, the conventional technology cannot improve the deformation by longitudinal extension sufficiently. In a case where a portion of such an image is enlarged and displayed, the image of which quality is insufficiently improved is enlarged. Therefore, the image quality is further deteriorated.